The invention relates to a method for synthesis of bibenzyl systems with nitro groups as substituents. Such compounds are important intermediates for pharmaceuticals.
According to the method toluene derivates with nitro groups, preferably in o- or p-position, are coupled oxidatively with air (oxygen) in methanolic KOH-solution under influence of small amounts of metal catalysts.
Several methods for the synthesis of nitrobibenzyl systems are known: ##STR1## This method needs handling of KOtBu or NaOEt. The best yield, about 70%, was reached by bubbling oxygen through the reaction mixture. The recovery of the product needs handling of ether and without equivalent amount of iso amyl formiate the yield will come down to 40%. Using NaOMe about 55% is obtained. KOtBu must be used in ether. The reaction time is long, about 24 hours at 0.degree. C. ##STR2## Pure oxygen must be used. The yield is low, about 30%. Ethylene diamine is a catalyst. ##STR3## Yields 51-60%. The reaction time is short but large amounts of liquid ammonia must be used. NaNH.sub.2 is prepared in situ from NH.sub.2. It is a drawback that sodium must be handled.
The earlier methods have several drawbacks as in certain cases bad yields, handling of chemicals with risks for the environment and comparatively expensive raw materials.